1. Field of the Invention
The present invention relates to a fabrication method of a multilayered optical waveguide structure which has an optical waveguide layer formed from a polysilane composition containing polysilane, and also to a multilayered optical waveguide structure fabricated by this method.
2. Description of the Related Art
A polymer optical waveguide having a core layer and a surrounding cladding layer, each made of a polymer, can be supplied in a large sectional area and fabricated by a simple technique and at low cost. Because of such advantages, its practical application has been expected. Japanese Patent Laid-Open No. 2004-333883 proposes a polymer optical waveguide having a core layer and a cladding layer both made of a polysilane compound.
In the field of optical waveguides, they are used in combination with a multicore optical fiber ribbon. This has led to a demand for an optical waveguide which consists of plural superimposed optical wirings. Japanese Patent Laid-Open No. Hei 11-183747 discloses a method wherein polymer optical waveguide films are laminated using a double-sided adhesive sheet to make a three-dimensional polymer optical waveguide array.
In Japanese Patent Laid-Open No. 2005-17816, a method is disclosed in which a curable resin for a cladding, i.e., a UV-curing resin is used as an adhesive to bond plural waveguide films.
However, the method disclosed in Japanese Patent Laid-Open No. Hei 11-183747 needs a separate, double-sided adhesive sheet for bonding the polymer optical waveguide films, which increases a thickness of the laminate to problematically prevent reduction of a weight and a size thereof. Also, release sheets must be removed from the double-sided adhesive sheet in order to sequentially bond the polymer optical waveguide films. This increases a complexity of the fabrication method, making it unsuitable for practical application.
In the method disclosed in Japanese Patent Laid-Open No. 2005-17816 which uses a liquid-form UV-curing resin as an adhesive, it is required that the UV-curing resin be first applied onto any of polymer optical waveguide films and, after they are bonded together, exposed to an ultraviolet light to cure the resin. This raises a problem of an increased complexity of the fabrication method. Also, this UV-curing resin is used as a cladding layer. Unless the UV-curing resin is applied properly, the resulting poor adhesion thereof to a core layer results in the problematic formation of air gaps between the core layer and the cladding layer.